1. Field of the Invention
This invention generally relates to a combustion gas powered tool, and specifically relates to a combustion gas powered fastener driving tool such as a combustion gas powered tacker or nailer.
2. Description of the Prior Art
U.S. Pat. No. 4,773,581 discloses a combustion gas powered tool or a combustion gas powered nailer which has grilles disposed in a cylindrical combustion chamber and extending perpendicular to the axis of the combustion chamber. The grilles serve to generate turbulences of an air-fuel mixture, promoting the combustion of the air-fuel mixture. In cases where an external fan is provided to smoothly scavenge burned gas from the combustion chamber, the grilles offer resistances to a flow of the burned gas. Therefore, the presence of the grilles causes an increased electric power of driving the fan. Since the fan driving power is supplied by a battery, the presence of the grilles causes a higher rate of the consumption of an electric power of the battery.
The combustion gas powered tool of U.S. Pat. No. 4,773,581 has communication holes extending through side walls of a cylinder. During a later stage of the movement of a piston from its top dead center to its bottom dead center, the burned gas is allowed to escape from the combustion chamber into atmosphere via the communication holes so that the pressure in the combustion chamber drops to an atmospheric level. Then, the gas remaining in the combustion chamber cools, and a vacuum occurs in the combustion chamber. After the piston reaches its bottom dead center, the vacuum in the combustion chamber helps the return of the piston to its top dead center.